Filtering apparatus is commonly used in swimming and spa pools for filtering the water in such pools. The apparatus which is in use is in a number of different forms ranging from cartridge type filters to sand and diatomaceous earth filters. Each type of filter is required to be regularly cleaned to maintain the efficiency of the filtering operation and also to ensure that excessive pressure loadings are not applied to the circulating pump. In the case of cartridge type filters, the filter is required to be disassembled, the filter cartridge removed and cleaned before reassembly. In the case of sand or diatomaceous earth filters, cleaning is accomplished by backwashing, that is by causing the flow of water to pass in a reverse direction through the filter to displace collected dirt from the filter material. Often backwashing is only carried out when the filter is substantially blocked and is normally achieved manually by operation of a valve to effect a reversal in the flow of the water. Usually also, the latter filters are required to be disassembled at regular intervals and recharged with sand or diatomaceous earth. The cleaning procedures described above are tedious and time consuming. Additionally, if these filters are not regularly cleaned, the efficiency of filtering is substantially reduced which, for example, reduces the efficiency of vacuum pool cleaners.
Liquid filtering apparatus is also used in many other applications for cleaning a liquid supply, for example, in irrigation systems where water is required to be filtered to prevent blockage of water sprinklers or the like. This form of apparatus also is required to be regularly cleaned to maintain cleaning efficiency.